1. Field of the Invention
This invention relates to a group of pharmaceutically acceptable amino-carboxylic acids and their amide derivatives and to pharmaceutical uses for these compounds. More particularly the invention pertains to the use of these compounds as anticonvulsant, sedative and anxiolytic agents in mammals.
2. Description of the Prior Art
Certain induced, recurrent, generalized seizures in mammals can be prevented by the administration of glutamine (GLN). These seizures have been thought to be related to the depletion of brain glutamine and its product gamma-amino-butyric acid (GABA), which is known to be a major inhibitory neurotransmitter substance acting between the nerve cells in the brain. Decreased GABA in the brain causes seizures. A precursor of GABA is the amino acid glutamine. GABA itself cannot be used clinically to prevent seizures because it does not cross the blood-brain barrier and has serious side effects (hypotension, shock, mortality). Glutamine is metabolized too quickly to be pharmacologically effective.
Several investigators have indicated that the use of GABA agonists given systemically is not associated with a useful anti-convulsant effect. For example, Meldrum (in an article published in The Lancet, Aug. 5, 1978, at p. 304-306) teaches that diffuse activation of GABA receptors by GABA or a GABA agonist given systemically does not provide a useful anticonvulsant effect. An article by Tsuchiya et. al., in Journal of the Physiological Society of Japan, 22,70-74 (1960) reports on the intraperitoneal administration to mice of GABA and delta-amino valeric acid (DAVA) in Tyrodes solution buffered at pH 7.4 ten minutes before inducing convulsions by the application of electroconvulsive shock. The reported results clearly demonstrate that as administered by the authors DAVA is ineffective in preventing or inhibiting convulsions. After initial testing the compound was dropped from subsequent anticonvulsant trials as reported in the article.
It has now been unexpectedly discovered contrary to the results obtained by Tsuchiya et al that DAVA has strong anticonvulsant properties, but only when administered in a form and under conditions markedly different from those used by Tsuchiya et al. Those authors used DAVA under conditions which favored a GABA mimetic role (neutral pH, activity within 10 minutes of injection). We have discovered that DAVA works not as a GABAmimetic but by a totally different action, namely "glutamine sparing". It has also been found that DAVA's anticonvulsant activity is delayed after administration. If they are to provide a useful anticonvulsive effect, the active agents of the present invention must be administered at least 30 minutes prior to the onset of a convulsive episode or seizure. It has also been found that the maximum anticonvulsant effect is achieved if the active agents of the invention are orally administered in coated solid dosage form having a pH between about pH 1.8 and 6.0, and preferably between pH 1.8 and pH 4.0. The reason for the decreased efficacy above pH 6.0 is not fully understood.
It has also been surprisingly found that the active amino acid compounds of the invention are particularly useful as anxiolytic agents in mammals when they are orally administered in the form of their acid addition salts.
Accordingly, it is an object of the present invention to provide a method of preventing seizures, and particularly epileptic seizures in mammals.
Another object of the present invention is to provide pharmaceutical dosage forms containing amino acid compositions which are analogs of glutamine, thus making more glutamine available for conversion to GABA.
Still another object of the present invention is to provide solid pharmaceutical formulations comprising an effective amount for inhibiting the onset of seizures of an amino acid composition or an acid addition salt thereof in a coated oral dosage form at a pH between 1.8 and 6.0.
A further object of the present invention is to provide an effective method of administering the anti-convulsant compositions disclosed herein.
A further aspect of the present invention is to provide effective sedative compositions.
These and other aspects of the invention will be apparent from the following description.
Convulsive disorders (e.g. epilepsy, seizures, fits, convulsions) have in common the occurrence of brief episodes. These episodes are associated with loss or disturbance of consciousness. Such episodes are usually but not always associated with characteristic body movements, and sometimes with autonomic hyperactivity. They are generally correlated with abnormal EEG discharges. The etiology of such disorders is varied and includes, e.g., genetic diseases, metabolic dysfunction, tumors and trauma.
The amino acids found to be useful as anti-convulsant and anxiolytic agents in the present invention may be generally described as aliphatic compounds in which the carboxylic acid and primary amine are separated by three or four units constituting a simple or substituted alkane, an ether or thioether, or an amide forming the backbone of a straight or branched chain molecule. The aminocarboxylic acids are either free acids or an amide and/or ester derivative of the acid.
The active compositions of the present invention are represented by the following general formula: ##STR1## wherein R.sub.1 is H, ##STR2## A is H, CH.sub.3, CH.sub.3 CH.sub.2 --, HO--CH.sub.2, HO--CH.sub.2 CH.sub.2, CH.sub.3 OCH.sub.2 --HS--CH.sub.2 --, HS--CH.sub.2 CH.sub.2 --, CH.sub.3 SCH.sub.2 --,
Y is C.dbd.O, HC--OH or, CH--A, PA1 Z is CH--A, O, S; or NH only if Y is C.dbd.O, and PA1 R.sub.2 is --OH, --NH.sub.2 or CH.sub.3 --CH.sub.2 --O--, PA1 n is 0 or 1, and Y is CH--A when n=0; and PA1 A+Y+Z include no more than one Oxygen or Sulfur atom
The preferred anti-convulsant of the present invention is DAVA or delta aminovaleric (5-aminopentanoic) acid of the formula: ##STR3##
Aside from its anxiolytic and anticonvulsant activity, DAVA and other compounds of the general formula have been found to posess sedative properties when administered in effective amounts for this purpose.
It has been found desirable to administer DAVA and the other compositions of the invention at a pH of between 1.8 and 6.0. This pH can be achieved by co-administering DAVA or DALA with a pharmaceutically acceptable buffering agent, e.g. organic or inorganic acid, or acid salt. Generally DAVA and the other compounds of the invention are administered in the form of the free acid and preferably in the form of their organic or inorganic acid addition salts. The preferred acid addition salt is DAVA hydrochloride. Additional pharmaceutically acceptable inorganic addition salts useful in the invention include sulfates, phosphates, and carbonates (e.g. DAVA carbonate, DALA phosphate). Illustrative organic acid addition salts of the active ingredients of the present invention include the citrate, lactate, acetate, and fumarate salts (e.g. DAVA citrate).
In considering the substituents of the general formula described above it is noted that only a single oxygen or sulfur atom is present in A, Y and Z. The preferred constituent of the R.sub.1 group is hydrogen although acetyl ##STR4## is also desirable at this position. Besides the R.sub.1 groups shown to be useful in the general formula, acyl groups derived from other simple metabolizable organic acids such as, citric, or butyric acid have been found useful.
As constituent A of the general formula hydrogen is the preferred moiety. However, compounds in which A is a CH.sub.2 --OH group have been found to perform almost as well as those which contain the H moiety.
In addition to the moieties enumerated in the general A formula set forth above, anxiolytic and anticonvulsant activity has also been found in compounds of the general formula wherein the A constituent is selected from groups having homologous side chains with 3 or 4 carbons in a straight or branched chain configuration. Representative of this class of constituents is 5-amino-4 hydroxy octanoic acid.
The preferred constituents of the Y and Z groups is CH.sub.2, which is especially preferred. As to the Z groups, it should be noted that NH may only be present at this position when the Y constituent is &gt;C.dbd.O.
Hydroxy (--OH) is the especially preferred constituent at the R.sub.2 position in the general formula for the present pharmaceutical compounds, although amino (--NH.sub.2) is also a preferred R.sub.2 constitutent. Compounds in which other esters and amides (e.g. peptides) are constituent R.sub.2 have shown some anticonvulsant activity, but are not believed to offer any particular benefit or advantage over those in the general formula.
In addition to DAVA, the preferred active agent of the present invention, 5-amino-4-oxo-pentanoic acid, 2-aminoethoxy acetic acid, 2-aminoethylthio acetic acid, and 5-amino-4-hydroxy pentanoic acid, also display anticonvulsant and anxiolytic properties in animals.
Although principal use of the compounds of the invention is anticipated to be as orally administered pharmaceutical agents for prevention, inhibition, and arrest of epileptic discharges in humans, the desirable sedative properties of DAVA are also of great significance. This is particularly true in view of the relatively non-toxic nature of the present compounds and the fact that they may be synthesized at relatively low cost.
The compositions of the present invention are preferably administered in a solid dosage form via the oral route. Although parenteral administration by subcutaneous, intramuscular and intravenous injection is also effective, the improved efficacy obtained at low pH makes this a less desirable route of administration in large mammals as it causes local irritation at the administration site and can lead to erythruria. Due to the highly acid pH of the active ingredient it is unsatisfactory to administer it alone via the oral route. The active ingredient in the oral dose preferably is administered in the form of a coated tablet, pill, beadlet, capsule, or other solid dosage unit. The coating or protective capsule is required to prevent the highly acid active ingredients from damaging the delicate tissues of the buccal cavity or the pharynx during administration. Suitable coatings may be prepared from an aqueous suspension containing sugar and insoluble powders such as starch, calcium carbonate, talc or titanium dioxide, suspended by means of acacia or gelatin. Waterproofing coatings consisting of substances such as shellac, cellulose acetate phthalate may be applied to a pill or talbet from a nonaqueous solvent and prior to the application of a sugar coat. Film coatings consisting of water soluble or dispersible materials such as hydroxypropylmethylcellulose, methylcellulose, carboxymethylcellulose sodium, and mixtures of cellulose acetate phthalate and polyethylene glycols applied out of nonaqueous solvents are also useful in coating the tablets and pills made according to the invention. Soft shell (gelatin) capsules of the type which do not dissolve until reaching the acidic environment (approximately pH 1.0-3.0) of the stomach are also useful as dosage forms in the invention. However, the capsules may comprise any well known pharmaceutically acceptable material such as gelatin, cellulose derivatives and the like. The active ingredients may be compounded in the desired oral form in combination with inert ingredients including fillers such as talc, lactose, starch, bentonite and diatomaceous earth; lubricants and food flavorings. Tablets for use in the invention may be made by punching or compressing the active ingredients on a tabletting machine.
Liquid oral doses in the form of solutions, and suspensions are also contemplated by the invention as are suppositories for rectal administration. In making solutions and suspensions the active ingredients may be dissolved or suspended in distilled water, conventional U.S.P. syrup formulations or any other pharmaceutically acceptable carrier liquid. For parenteral administration the compounds of the invention are preferably dissolved in distilled water, isotonic saline solution or any other pharmaceutically acceptable carrier liquid.
Several of the (4-) and (5-) amino carboxylic acid compounds in this series are commercially available. They include among others, 5-aminopentanoic acid, 5-aminolevulinic acid, and glycylglycine, all available from Sigma Chemical Company, St. Louis, Mo.
The other compounds of the general formula can be directly prepared by conventional synthetic procedures or using processes described in the literature. Thus, 2-aminoethoxy-acetic acid may be prepared according to the synthesis taught in Academie des Sciences, Paris. Comptes Rendus Hebdomadaires des Seances (Compt. Rend.) 234, 1980 (1952), CA 47,2761e. 5-amino-hexanoic acid can be synthesized by the method in Ricerca Scientifica l, IIA, 312 (1961), CA57,9658h. 5-amino-4-hydroxy-pentanoic acid is prepared by reduction of 5-aminolevulinic acid using the procedure taught in Biochemical Biophysical Research Communications 39, 135 (1970); and 4-amino-5-hydroxy-pentanoic acid, synthesized by the method in Biochemica Biophysica Acta 8, 287 (1952), CA 47, 4843d. Other compounds of the invention such as 2-acetoxy-1-propylamine, 1-acetoxy-2-propylamine, 2-acetoxy-1-butylamine, 1 acetoxy-2 butylamine and 2-amino-ethylthio-acetic acid are prepared by adaptation of the method for preparing 2-amino ethoxyacetic acid (taught in the Compt. Rend. article referred to above) by substituting, respectively, in the synthesis of each of the above amino acids: 1-amino-2-propanol, 2-amino-1-propanol, 1-amino-2-butanol, 2-amino-1-butanol and 2-amino-ethylthiol.
It is to be understood that where an amino acid compound described in the art is identical with one of the above specified named compounds, but has been known by another name by reason of isomerization or production in accompaniment with other compounds, the identification of such substances by the name set forth above is intended to identify the same compound under all other designations.
When used as anticonvulsant or sedative agents in mammals, the active agents present compositions are administered at a dosage level of from about 0.03 to about 40 mmol (3.5-4680 mg, and preferably 50-200 mg.) of active ingredient per kilogram of body weight per day. The daily effective dosage, or the dosage required to prevent or inhibit convulsions from a particular disease or stimulus, or to achieve sedation depends upon the condition being treated, the individual characteristics of each mammal being treated and the nature of the physical or chemical stimulus inducing or responsible for the convulsive activity. Thus, the exact dose required to alleviate convulsions attributable to a particular disorder or stimulus, or to their effects will vary within the dosage range, discussed above from one patient to another. The anxiolytic properties of the present compounds are evident in the same dosage ranges employed for anticonvulsant treatment. Sedative properties of the present agents are apparent at the higher end of the dosage levels discussed above (e.g. dosages of between about 10 and 40 mmol active ingredient per kilogram of body weight are sedative dosages). Within the stated dosage ranges, the effective dose for small mammals (e.g. mice) is approximately 10 times the effective dose for larger mammals (e.g. cats, dogs, humans).
Solid pharmaceutical dosage forms such as pills, capsules, and tablets may contain from 5 to about 750 milligrams of active ingredient. Preferably from about 50 to about 500 milligrams of active ingredient is incorporated in each solid dosage form together with the required amount of buffer material if any is required, to bring the pH of the dosage to between pH 1.8 and pH 6.0.
The liquid dosage forms of the present invention are preferably administered in the form of a solution or suspension in a pharmaceutically acceptable vehicle, preferably distilled water. Liquid dosages containing from about 5 to about 100 milligrams of active ingredient per cubic centimeter of vehicle have been found to be useful in administering these agents to mammals. The preferred concentration within this range will depend upon the age and weight of the subject being treated.
It is also contemplated that the anti-convulsant agents of the invention may be administered in the form of rectal suppositories. Suitable suppository dosage forms may be prepared by incorporating the active agent into a shapeable base material. Among the suppository bases that can be used to prepare suppositories according to the present invention are cocoa butter, glycerinated gelatin, hydrogenated vegetable oils, mixtures of polyethylene glycols of various molecular weights, and fatty acid esters of polyethylene glycol. Rectal suppositories for adults are tapered at one end, usually weigh about 2-4 grams and may contain from about 5 to about 500 milligrams of active ingredient. Preferably such suppositories are made from one or more bases having a melting point that will enable them to melt or dissolve slowly upon retention in the rectal cavity.
The anticonvulsant activity of the instant aminocarboxylic acid compounds was measured against seizures produced in female DBA/2J mice using: L-methionine-RS-sulfoximine (MSO), 100 mg/Kg injected subcutaneously (SC), pentylenetetrazole (PTZ), 65 mg/Kg, SC or electroconvulsive shock (ECS), 18 mA at 380 V for 0.1 sec. These are standard test conditions which produce convulsions in 90-100% of saline injected (control) animals. Anticonvulsant activity was also tested using supramaximal ECS which produces tonic extension seizures in 100% of control animals.
In testing representative compounds of the invention for anti-convulsant activity Glycylglycine (Glygly), Glycine (Gly), Glutamine (Gln), 5-amino-valeric acid (DAVA) and 5-amino-levulinic acid (DALA) were administered to the DBA/2J animals SC at 15 mmol/kg body weight or orally at 30 mmol/kg of body weight. The active ingredients were injected or administered 45 minutes after MSO injection or 60 minutes before PTZ or ECS administration. Saline injected controls were treated in parallel with those animals receiving an active dose. In some instances GlyGly injected animals and saline controls were given ECS after 180 minutes.
An important aspect of the present invention involves administration of the active anti-convulsant substantially prior to the application or onset of the convulsive stimulus or attack. Generally the active agent should be administered from at least 30 minutes to 4 hours or more before application or onset of the seizure stimuli whose inhibition is sought. The interval between administration of the agent and observation of its anticonvulsant effect is believed to be attributable to the fact that the mode of action of these agents is to spare glutamine, a GABA precursor, thus making more glutamine available for the production of GABA. During this latency, the glutamine which has been spared must travel to the pre-synaptic terminals of the neurons where it is metabolized to GABA. Glutamine also plays an important role in other metabolic processes in the brain. Thus, the mechanism of action of the active compounds in the present invention is believed to be different than for prior art anticonvulsant agents which directly affect the ability of the synapses to transmit neural impulses.
For administration via the parenteral route in mice, the acid compounds (pH 1.8-6.0, preferably pH 1.8-4.0) of the invention were injected subcutaneously, in isotonic saline solution, at a dose of 15 mmol/Kg body weight. Anti-convulsant activity against seizures produced by MSO or PTZ was determined by measuring the difference in time to onset of seizures between experimentally treated animals and saline injected control animals. The effectiveness against ECS seizures was measured on a four point scale with seizure severity being scored as follows: Seizure with full extension and death, 3; seizure will full extension, 2; clonic seizure without tonic extension, 1; no seizure, 0. Dosage and time data were obtained using supramaximal ECS which produces toxic extension seizures in 100% of control (saline injected) animals.